IDO Vaccine Ablates Immune-Suppressive Myeloid Populations and Enhances Antitumor Effects Independent of Tumor Cell IDO Status.

The immunosuppressive tumor microenvironment (TME) does not allow generation and expansion of antitumor effector cells. One of the potent immunosuppressive factors present in the TME is the indoleamine-pyrrole 2,3-dioxygenase (IDO) enzyme, produced mainly by cancer cells and suppressive immune cells of myeloid origin. In fact, IDO+ myeloid-derived suppressor cells (MDSC) and dendritic cells (DC) tend to be more suppressive than their IDO- counterparts. Hence, therapeutic approaches that would target the IDO+ cells in the TME, while sparing the antigen-presenting functions of IDO- myeloid populations, are needed. Using an IDO-specific peptide vaccine (IDO vaccine), we explored the possibility of generating effector cells against IDO and non-IDO tumor-derived antigens. For this, IDO-secreting (B16F10 melanoma) and non-IDO-secreting (TC-1) mouse tumor models were employed. We showed that the IDO vaccine significantly reduced tumor growth and enhanced survival of mice in both the tumor models, which associated with a robust induction of IDO-specific effector cells in the TME. The IDO vaccine significantly enhanced the antitumor efficacy of non-IDO tumor antigen-specific vaccines, leading to an increase in the number of total and antigen-specific activated CD8+ T cells (IFNγ+ and granzyme B+). Treatment with the IDO vaccine significantly reduced the numbers of IDO+ MDSCs and DCs, and immunosuppressive regulatory T cells in both tumor models, resulting in enhanced therapeutic ratios. Together, we showed that vaccination against IDO is a promising therapeutic option for both IDO-producing and non-IDO-producing tumors. The IDO vaccine selectively ablates the IDO+ compartment in the TME, leading to a significant enhancement of the immune responses against other tumor antigen-specific vaccines.

Building the Next Generation of Humanized Hemato-Lymphoid System Mice.

Since the late 1980s, mice have been repopulated with human hematopoietic cells to study the fundamental biology of human hematopoiesis and immunity, as well as a broad range of human diseases in vivo. Multiple mouse recipient strains have been developed and protocols optimized to efficiently generate these "humanized" mice. Here, we review three guiding principles that have been applied to the development of the currently available models: (1) establishing tolerance of the mouse host for the human graft; (2) opening hematopoietic niches so that they can be occupied by human cells; and (3) providing necessary support for human hematopoiesis. We then discuss four remaining challenges: (1) human hematopoietic lineages that poorly develop in mice; (2) limited antigen-specific adaptive immunity; (3) absent tolerance of the human immune system for its mouse host; and (4) sub-functional interactions between human immune effectors and target mouse tissues. While major advances are still needed, the current models can already be used to answer specific, clinically-relevant questions and hopefully inform the development of new, life-saving therapies.

Manipulating the function of tumor-associated macrophages by siRNA-loaded lipid nanoparticles for cancer immunotherapy.

The tumor-microenvironment contains large numbers of tumor-associated macrophages (TAMs) which are largely M2 phenotypes and are involved in pro-tumorous functions. Targeting TAMs so as to manipulate them and to modify their functions could be a novel immunotherapy for the treatment of cancer. Such a strategy would involve targeting TAMs with short interfering RNA (siRNA) to modify their functions by silencing certain genes that are responsible for their M2 polarization. In this study, a lipid nanoparticle (LNP) formulation was used to target and deliver siRNA to TAMs. The LNP was mainly composed of a novel, pH-sensitive cationic lipid, referred to as the CL4H6 lipid, which had previously been optimized to target hepatocytes. The optimized siRNA-loaded CL4H6-LNPs were selectively and efficiently taken up and showed strong gene silencing activity in TAMs in a human tumor xenograft model in nude mice. Furthermore, an anti-tumor therapeutic response in the same tumor model was obtained by targeting TAMs using the optimized siRNA-loaded CL4H6-LNPs. The anti-tumor therapeutic response was obtained through the silencing of the signal transducer and activator of transcription 3 (STAT3) and hypoxia inducible factor 1 α (HIF-1α), which resulted in an increase in the level of infiltrated macrophage (CD11b+ cells) into the tumor-microenvironment (TME) as well as a tendency to increase the concentration of M1 macrophages (CD169+ cells). The treatment also resulted in reversing the pro-tumorous functions of TAMs -mainly angiogenesis and tumor cell activation-, as evidenced by a decrease in the related gene expression at the mRNA level. This research has promising clinical and pharmaceutical applications for achieving novel macrophage-based cancer immunotherapy.

Mixing lipids to manipulate the ionization status of lipid nanoparticles for specific tissue targeting.

INTRODUCTION: The development of targeted drug delivery systems is a rapidly growing area in the field of nanomedicine. METHODS: We report herein on optimizing the targeting efficiency of a lipid nanoparticle (LNP) by manipulating the acid dissociation constant (pKa) value of its membrane, which reflects its ionization status. Instead of changing the chemical structure of the lipids to achieve this, we used a mixture of two types of pH-sensitive cationic lipids that show different pKa values in a single LNP. We mixed various ratios of YSK05 and YSK12-C4 lipids, which have pKa values of 6.50 and 8.00, respectively, in one formulation (referred to as YSK05/12-LNP). RESULTS: The pKa of the YSK05/12-LNP was dependent not only on the molar ratio of each lipid but also on the individual contribution of each lipid to the final pKa (the YSK12-C4 lipid showed a higher contribution). Furthermore, we succeeded in targeting and delivering short interfering RNA to liver sinusoidal endothelial cells using one of the YSK05/12-LNPs which showed an optimum pKa value of 7.15 and an appropriate ionization status (~36% cationic charge) to permit the particles to be taken up by liver sinusoidal endothelial cells. CONCLUSION: This strategy has the potential for preparing custom LNPs with endless varieties of structures and final pKa values, and would have poten tial applications in drug delivery and ionic-based tissue targeting.